In laser processing, there is a so-called remote welding method for condensing a laser beam in a distance from a laser oscillator to perform welding while using a condenser lens having a long focus. A processing laser condensed by the condenser lens having a long focus can perform processing of a degree same as that of processing in a focus position even in a position slightly deviating from the focus position. In other words, since it is possible to secure long focal depth in a thickness direction of a workpiece, it is unnecessary to perform strict focus position management.
Incidentally, in order to condense the processing laser in a distance from the laser oscillator, a relatively high-quality laser oscillator is necessary. However, in the past, a laser oscillator that irradiates a carbon dioxide laser is mainly used. Since the carbon dioxide laser cannot be guided by an optical fiber, when it is attempted to condense the carbon gas laser in a distance like a welding area in a vehicle from the laser oscillator on the outside of the vehicle, a large number of mirrors have to be provided. Therefore, there is a problem in that it takes time to adjust the mirrors and cost increases. For the laser oscillator that irradiates a carbon dioxide laser, a technique for guiding the laser with an optical fiber has been developed. According to this technique, even when the laser is condensed in a distance like a welding area in a vehicle, it is possible to guide the laser using free flexibility of the optical fiber, it is unnecessary to adjust mirrors and the like, and, moreover, it is possible to reduce cost.
In a process of applying the remote welding method by a laser beam of this optical fiber light-guide type, it is becoming necessary to more strictly perform focus position management for the processing laser compared with the past. One of causes for this is considered to be that, in condensing an optical fiber light-guide type laser beam, since an optical system for focusing an emission fiber end face of the optical fiber is formed, beam shapes are different in a focus position and the periphery of the focus position.
In the laser processing, whichever of the carbon dioxide laser beam and the optical fiber light-guide type laser beam is applied, a focus position of the processing laser cannot be visually recognized. Therefore, in the present situation, visually recognizable focus positions of plural visible lasers are caused to coincide with the focus position of the processing laser in advance, the focus position of the processing laser is simulated by visually focusing the respective visible lasers, and laser processing is performed.
In order to improve visual focusing operation of the visible lasers, a technique for a teaching method and apparatus in a laser beam machine for irradiating one auxiliary laser beam (visible laser) and a main laser beam for processing on a work through an identical condenser lens and setting a point where both the laser beams coincide with each other as a focus position is disclosed in Patent Document 1. Moreover, a technique for a laser processing apparatus and a distance adjusting method for performing adjustment of a separation between a print surface of a work and a laser beam (print light) on the basis of an indication image formed by an intersection of two visible lights is disclosed in Patent Document 2.
Patent Document 1                JP Patent Publication (Kokai) No. 10-58169 A        
Patent Document 2                JP Patent Publication (Kokai) No. 2005-131668 A        